Internally Located Return Electrode Electrosurgical Apparatus, System and Method

ABSTRACT

A bipolar, plasma-generating electrosurgical apparatus and system wherein the return electrode is enclosed within an electrosurgical shaft, and the active electrode is located on the outside surface of the shaft such that in treating the tissue, the tissue is exposed to plasma generated on the active electrode, but is minimally exposed to electric fields generated between the active and return electrodes. Due to the configuration of the electrodes, electric fields generated between the electrodes are directed away from the target tissue and inwardly towards the return electrode within the shaft, thereby electrical stimulation of neuromuscular structures in the tissue by the electric fields is minimized.

RELATED APPLICATION

This application is a continuation-in-part of U.S. patent applicationSer. No. 11/367,254 filed Mar. 2, 2006, the complete disclosure of whichis incorporated herein by reference for all purposes.

FIELD OF INVENTION

This invention pertains to an electrosurgical apparatus, system andmethod of treating tissue in a body structure, in particular a bipolar,plasma-generating electrosurgical apparatus and system wherein thereturn electrode is enclosed within an electrosurgical shaft, and theactive electrode is located on the outside surface of the shaft suchthat in treating the tissue, the tissue is exposed to plasma generatedon the active electrode, but minimally exposed to localized electricfields generated between the active and return electrodes. In variousembodiments, due to the configuration of the electrodes, the electricfields are directed away from the target tissue, as they are orientedinwardly towards the return electrode within the shaft, thereby avoidingelectrical stimulation of neuromuscular structures in the tissue bythese electric fields.

BACKGROUND

Electrosurgical instruments and systems comprising an active and returnelectrode and powered by a radio-frequency voltage supply as isillustrated for example in FIG. 1, are widely used in procedures fortreating target tissues in the body. Treatment of the target tissueinvolves placing the electrodes (10) in close proximity to a targettissue (12) and applying power to the electrodes to cause Coblation™,heating, ablation, coagulation, cutting, removal, puncturing, probing,and otherwise stimulating the tissue. In some systems an electricallyconductive fluid is supplied between the electrodes to generate plasmato treat the tissue; in other systems, the body's fluids are used as theconductive fluid. An example of such system for treating tissues withplasma is described in commonly assigned U.S. patent application Ser.No. 10/661,118, (Attorney Docket no. A-21-1), hereby incorporated hereinby reference for all purposes.

In an electrosurgical system as illustrated in FIG. 1, the electrodesare located on the distal end portion of the shaft (14). In oneconfiguration of the distal end portion of the shaft as is illustratedin detail FIG. 2, the return electrode (16) is positioned on the outsideperimeter of the shaft and, in various embodiments, surrounds the activeelectrode (18) which is within the shaft. To ensure that plasma (20)generated on the active electrode is closest to the tissue, the distaltip of the active electrode projects beyond the return electrode. Also,in the embodiment illustrated in FIG. 2, the active electrode isseparated from the return electrode by an insulator (24), andelectrically conductive fluid (22) is supplied between the electrodes bya fluid lumen (26) circumferentially positioned on the shaft around thereturn electrode. This conductive fluid as is illustrated in FIG. 2forms a conductive fluid pathway (38) between the electrodes

Also in an electrosurgical system as is illustrated in FIG. 2 and aswill be appreciated by one ordinarily skilled in the art, when power isapplied across the electrodes, an electric field (22) sometimes in theorder of 30,000 V/cm is generated which, for some procedures, is notdesired as these fields can interact with the tissue and causeelectrical stimulation of neuromuscular structures (28) within thetissue.

Accordingly, there is a need for apparatus and systems for use inelectrosurgical procedures wherein unwanted electrical stimulation ofthe tissue is avoided, and which can be used in confined spaces withinthe body.

SUMMARY OF THE INVENTION

The present electrosurgical apparatus in one embodiment comprises anelectrosurgical shaft having a proximal end portion and a distal endportion. The shaft includes an active electrode disposed on the surfaceof the distal end portion, and a return electrode disposed within thedistal end portion of the shaft. Positioned between the active andreturn electrode is an insulating member that prevents direct electricalcontact between the active and return electrodes. The shaft includes aninterconnecting passageway within the distal end portion of the shaftbetween the active and return electrode. The electrodes are connected toa radio-frequency voltage supply by connectors such that on applying aradio-frequency voltage difference across the active and returnelectrodes, plasma is generated on the active electrode, and electricalfields generated between the electrodes are directed from the activeelectrode to the return electrode in the shaft, to avoid electricalstimulation of the tissue. The plasma can be used to treat the tissue bycoblating, heating, ablation, coagulation, cutting, removal, puncturing,probing, and otherwise stimulating the tissue.

The present electrosurgical system in one embodiment is a system forperforming an electrosurgical procedure on a body tissue using plasmasuch that electrical stimulation of the tissue is minimized, the systemcomprising: an electrosurgical instrument comprising a shaft; anelectrically conductive fluid supply having a discharge port on a distalend of the shaft; and a radio-frequency voltage supply connected to theelectrosurgical instrument. In one embodiment, the shaft comprises: anactive electrode on the distal end; a return electrode recessed withinthe shaft; an electrical insulator separating the active and returnelectrode. Within the shaft is a chamber in communication with theactive and return electrodes such that on applying the radio-frequencyvoltage supply to the active and return electrodes in the presence of anelectrically conductive fluid, plasma is generated on the activeelectrode on the surface of the shaft, and electric fields generatedbetween the active and return electrodes are directed within the shaft,and thus away from the tissue. In some embodiments the shaft of theelectrosurgical instrument may include an aspiration lumen having aplurality of inlet apertures formed along a selected length of theshaft, where the selected length of the shaft include a first portionfor insertion within a target tissue structure, such as anintervertebral disc, and a second portion for venting outside the targettissue structure.

The present electrosurgical method in one embodiment is a method oftreating tissue that avoids nerve stimulation, comprising the steps of:positioning a distal end of an electrosurgical instrument in closeproximity to the tissue, the distal end comprising an active electrodeand a return electrode; applying a radio frequency voltage across theactive and return electrodes in the presence of an electricallyconducting fluid sufficient to generate plasma on the active electrode;and contacting the tissue with the plasma such that the tissue isexposed to plasma but minimally exposed to electric fields generatedbetween the active electrode and the return electrode.

In various embodiments the present apparatus and system can be used inprocedures for treating highly neutralized tissue, and other tissueslocated in confined targets within the body. An example of such targetsis tissue in the intervertebral discs.

Details of embodiments of the present apparatus, system and methods areillustrated and described the following Figures and specifications.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of a bipolar electrosurgical system.

FIG. 2 is an illustration of a cross-section of the distal end portionof an electrosurgical instrument showing plasma and electrical fieldsbetween the active and return electrodes.

FIG. 3 is an illustration of lateral view of a partial spinal column.

FIG. 4 is an illustration of a perspective view of an intervertebraldisc.

FIG. 5 is an illustration of an embodiment of the present apparatuswithin a herniated intervertebral disc for treating the disc inaccordance with one orientation of the apparatus.

FIG. 6 is an illustration of a perspective cut-away view of the distalend of the present electrosurgical shaft.

FIG. 7 is an illustration of a longitudinal cross-sectional view of thedistal end of the present electrosurgical shaft.

FIG. 8 is an illustration of the cross-section of the distal end portionof the present apparatus showing conductive fluid and electrical fieldsbetween the active and return electrodes, without plasma.

FIG. 9 is an illustration of the cross-section of the distal end portionof the present apparatus showing conductive fluid flow, electrical fieldlines between the active and return electrodes, with plasma on theactive electrode.

FIG. 10 is an illustration of a perspective view of an embodiment of thepresent active electrode.

FIG. 11 is as illustration the present electrosurgical system whereinthe return electrode is enclosed with the distal end of anelectrosurgical shaft.

FIG. 12 is an algorithm of the present method of treating tissue withthe present apparatus and system.

FIG. 13 shows an electrosurgical system for insertion according to thepresent disclosure for treating a target tissue.

FIG. 14 shows a cut-away view of a portion of a shaft of anelectrosurgical system.

FIG. 15 shows an enlarged view of the distal end of an electrosurgicalsystem, with portions removed, according to the present disclosure.

FIG. 16 shows an embodiment of an active electrode according to thepresent disclosure.

DETAILED DESCRIPTION

With reference to FIGS. 1 and 2, a plasma-generating bipolarelectrosurgical system typically comprises an electrosurgical shaft (14)having proximal (30) and distal (32) end portions; one or more activeelectrode(s) (18) located on the distal end of the shaft; a returnelectrode (16) located on the shaft of the return electrode andseparated from the active electrode by an insulator (24); electricalconnectors (34) coupling the active and return electrodes (18, 16) to asource of radio-frequency voltage supply (36); and a supply ofelectrically conductive fluid (26, 26 a) adapted to be dischargedbetween the active and return electrodes. On application of theradio-frequency voltage across the electrodes in the presence of theconductive fluid, plasma is generated which can be used to treat tissueas described for example in U.S. patent application Ser. No. 10/661,118,(Attorney Docket no. A-21-1), supra.

A bipolar electrosurgical apparatus, as is illustrated for example inFIGS. 1 and 2, is an electrosurgical apparatus wherein both the activeand return electrodes (18, 16) are positioned on the shaft (14). In thisregard, a bipolar apparatus is distinguishable from a monopolarapparatus in that on a monopolar apparatus only the active electrode ispositioned on the shaft; in a monopolar apparatus the return electrodeis located off the shaft but is in electrical contact through thepatient to the target site and the electrically conductive fluid.

Examples of an electrically conductive fluid include isotonic saline, aconductive gel, Ringer's solution and the biocompatible electrolytes asdescribed for example in U.S. patent application Ser. No. 10/661,118,(Attorney Docket no. A-21-1), supra.

In a bipolar electrosurgical apparatus as is illustrated for example inone embodiment in FIG. 2, the electrodes are separated from each otherby an insulator (242) to prevent short-circuiting of the electrodes onthe distal end portion of the shaft. However, to establish a closedelectrical circuit across the electrodes on the shaft and generateplasma, an electrically conductive fluid pathway (38) is providedbetween the electrodes. This electrically conductive fluid pathway canbe provided in several ways including placing the conductive fluid onthe shaft such that the fluid is in contact with both electrodes; orplacing the conductive fluid on the target tissue such that the fluid isin contact with both electrodes and the target tissue at the same time;or inserting the shaft into the tissue such that the electrical circuitbetween the electrodes is established through the tissue by conductivebody fluids in the tissue.

In both bipolar and monopolar plasma-generating apparatus, however,regardless of how the conductive pathway is established between theelectrodes, for the instrument to generate plasma it is necessary tomaintain a closed electrical circuit on the distal end of the shaftcomprising the electrodes, the electrically conductive fluid and thepower supply, as described for example in U.S. patent application Ser.No. 10/661,118, (Attorney Docket no. A-21-1), supra.

On a bipolar plasma-generating systems and apparatus as illustrated inFIGS. 1 and 2 and as is described in commonly assigned U.S. patentapplication Ser. No. 10/661,118, (Attorney Docket no. A-21-1), supra,plasma is generated on the electrodes by applying a radio frequencyvoltage across the electrodes in the presence of the electricallyconductive fluid (22, 38). With these systems and apparatus, plasma(20), comprised of energized charged species such as ions and electrons,is used to treat the target tissue by Coblation™ as described in U.S.patent application Ser. No. 10/661,118, (Attorney Docket no. A-21-1),supra.

On a plasma-generating bipolar apparatus, in order to generate and useplasma to treat the tissue, the electrodes are designed such that onlythe active electrode generates the plasma, and that in use thiselectrode is located as close as possible to the target tissue.Conversely, the return electrode is designed such that it does notgenerate plasma, and that in use it is away from the target tissue toavoid contacting the tissue, but it is in electrical contact with theactive electrode through the electrically conductive fluid. One way bywhich the plasma is generated on the active electrodes but not on thereturn electrode is to maintain the surface area of the active electrodesmaller relative to the surface area of the return electrode.

In this regard it should be noted that during use, ablated tissues andother materials may accumulate on the return electrode thereby causing areduction of its exposed surface area relative to the exposed surfacearea of the active electrode, thereby undesirably causing the returnelectrode to also generate plasma.

In a plasma-generating bipolar apparatus and system as is illustratedfor example in FIGS. 1 and 2 and described in U.S. patent applicationSer. No. 10/661,118, (Attorney Docket no. A-21-1), supra, a convenientway by which a relatively large return electrode is maintained is to usethe shaft proximal of the active electrode as the return electrode.Typically this involves using an outer metallic portion of the shaftthat is insulated from the active electrode. Thus, as is illustrated inFIG. 2 in a bipolar system, in one embodiment, the active electrode isthe distal tip of the shaft, whereas the return electrode is the shaft'souter surface insulated from the active electrode.

Also as is illustrated for example in FIGS. 1 and 2 and described inU.S. patent application Ser. No. 10/661,118, (Attorney Docket no.A-21-1), supra, in using a plasma-generating bipolar apparatus for someprocedures it is necessary to supply the electrodes with an electricallyconductive fluid to form the conductive pathway (22, 38) between theelectrodes (18, 16), and in some embodiments also to flush the targetsite and the electrodes with fluid.

In procedures requiring a conductive fluid, this fluid can be providedby a fluid supply lumen located on the shaft. In this arrangement thefluid supply lumen is attached to a conductive fluid supply at theproximal end, such that the fluid is available for discharge at thedistal end through an opening in the lumen near the electrodes and thetarget site.

Further, in a plasma-generating bipolar apparatus as is illustrated forexample in FIGS. 1 and 2, for some procedures it is necessary to removeexcess fluids and ablated tissue away from the target site. Where suchfluid and tissue removal is necessary, an aspiration lumen is provided.In various embodiments the fluid aspiration lumen is located on theshaft but it can also be placed off the shaft in other embodiments. Inan arrangement wherein the aspiration lumen is on the shaft, the lumenmay comprise of a fluid inlet port disposed at the distal end of shaft,and a fluid discharge port at the proximal end where it is connected toa vacuum system for suctioning fluids, gases and ablated tissue from thetarget site through the aspiration lumen.

One procedure wherein a bipolar, plasma-generating apparatus is used fortreating tissue is in treating an intervertebral disc as is describedfor example in U.S. patent application Ser. No. 10/656,597, (AttorneyDocket No. S-12) incorporated herein by reference herein for allpurposes. In one procedure as illustrated in FIGS. 3-5, the distal endof the shaft (40) is inserted in the disc (38) and thereafterradio-frequency voltage is applied across the electrodes to generateplasma to treat the disc. In FIG. 5, the wand (50) is shown insertedanteriorily into the disc, however as will be appreciated to oneordinarily skilled in the art, in other procedures not shown in FIG. 5,the wand is also insertable posteriorily into the disc.

As can be appreciated in the art in using a bipolar apparatus intreating a intervertebral disc as is illustrated in FIGS. 3-5, besidesgenerating plasma as described above, the apparatus also generateselectrical fields (22) across the electrodes as is illustrated in FIG.2, and these fields can be as high as 30,000 V/cm. A problem with theseelectrical fields is that in sensitive tissues such as in the disc andaround the spine, the electric fields can cause undesired stimulation ofregional nerve or nerve fibers (28) as is illustrated in FIG. 2.

Also as can be appreciated by one ordinarily skilled in the art, intreating tissue in confined spaces such as in the intervertebrate disc,it can be difficult to avoid contacting the tissue with the returnelectrode thus causing a short circuit across the electrodes or reducingthe surface area of the electrode relative to the area of the activeelectrode.

Another problem with using a bipolar apparatus in confined spaces suchas in the invertebrate disc is that since the shaft may include a fluidsupply lumen and an aspiration lumen, the shaft can get too bulky foreasy access and use.

Accordingly, the present apparatus, system and apparatus in variousembodiments are adapted to electrosurgically treat tissue, whileminimizing exposure of the tissue to electrical stimulation. Theapparatus, as will be appreciated from the present description, is alsoreduced in size in part because of the placement of the return electrodewith the shaft; thus, with a smaller profile on the distal end thepresent apparatus and system provides improved access flexibility forapplying electrosurgical procedures in restricted areas of the body, asfor example, within an intervertebral disc.

With reference to FIG. 5-11, in one embodiment the electrosurgicalapparatus (50) comprises a shaft (52) having a proximal end portion (54)and a distal end portion (56). On the distal end portion of the shaft isdisposed an active electrode (58) on the surface of the shaft. Alsodisposed on the distal end but within the shaft is a return electrode(60) that is insulated from the active electrode by an insulating member(62) positioned on the distal end portion of the shaft. In thisposition, the insulating member prevents direct electrical contactbetween the active and return electrodes. Also included in the shaft inthe present embodiment are electrical conductors (64, 66) that areadapted for applying a radio-frequency voltage difference across theactive and return electrodes.

In one embodiment the electrosurgical apparatus comprises a lumen (70)within the shaft through which an electrically conductive fluid such assaline, Ringer's solution or an other acceptable other biocompatibleionic solutions can be supplied to the distal end of the shaft in thevicinity of the electrodes and the target tissue. As is illustrated inFIGS. 1 and 11, the electrically conductive fluid can be supplied from areservoir (26A) attached to the apparatus at the proximal end; in otherembodiments not shown the reservoir is located on another apparatus.

In the embodiment illustrated in FIGS. 6-9, for example, the lumen isconnected to an interconnecting passage (68) formed within the distalend of the shaft in between the electrodes. Within this interconnectingpassage as is illustrated in FIG. 9, when a high frequency voltage usapplied across the electrodes in the presence of an electricallyconductive fluid, for example within the interconnecting passageway(68), plasma (74) which can be used to treat tissue is generated on theactive electrode (58). Also, as noted above, when the power is appliedto the electrodes, an electric field (76) is generated between theactive electrode (58) and the return electrode (76) located within theshaft (52). Thus, since these electric fields are directed inwards,their effect on neighboring tissue is at least minimized, or eliminated.

In an embodiment of the active electrode illustrated in FIGS. 6-10, andin particular in FIG. 10, a plurality of apertures or holes (78) areprovided on the electrode for passing an electrically conductive fluidbetween the outside of the shaft to the return electrode. In oneembodiment the apertures are in the form of a mesh made of interwovenwires. Thus with this embodiment, both electrodes can be kept inelectrical contact with an electrically conductive fluid within theinterconnecting passageway (68).

Also in the embodiment of the apparatus illustrated in FIGS. 6-10, thereturn electrode is connected to a conductive cap (76) having an exposedsurface on the outer surface of the shaft (52), such that the cap isspaced sufficiently far from the active electrode to minimize generationof an electric field between the active electrode and the cap. Anadvantage of using this cap is that if the cap is conductive, since itis connected to the return electrode, its conductive area contributes tothe area of the return electrode and thus have helps to ensure that thecharge density on the surface of the return electrode is lower than thecharge density on the surface of active electrode.

With reference to FIGS. 1 and 11, the electrosurgical apparatus in oneembodiment comprises an aspiration lumen having an inlet in theproximity of the electrodes for removing fluids form the distal endportion of the shaft. The fluids may include fluids that flush the siteas well as fluids that result from treatment of the tissue.

Also provided in the present application is a system for performing anelectrosurgical procedure on a body tissue using plasma, as isillustrated for example in FIG. 11. The system (50) in one embodimentcomprises an electrosurgical instrument comprising a shaft (52); anelectrically conductive fluid supply having a discharge port on a distalend (56) of the shaft; and a radio-frequency voltage supply (36)connected to the electrosurgical instrument. In one embodiment, and asdescribed above with reference to FIGS. 6-9, the shaft comprises: anactive electrode (58) on the distal end; a return electrode (60)recessed within the shaft; an electrical insulator (62) separating theactive and return electrode; and a chamber (68) in communication withthe active and return electrodes within the shaft, wherein on applyingthe radio-frequency voltage supply (78) to the active and returnelectrodes in the presence and electrically conductive fluid (72),plasma (74) is generated on the active electrode on the surface of theshaft, and electric fields (76) generated between the active and returnelectrodes are directed within the shaft.

Further provided is a method of treating body tissue includingnerve-sensitive tissue in the body, as set forth in FIG. 12, comprisingthe steps of: positioning a distal end of an electrosurgical instrumentin close proximity to the tissue (122), the distal end comprising anactive electrode and a return electrode; applying a radio frequencyvoltage across the active and return electrodes in the presence of anelectrically conduct fluid sufficient to generate plasma on the activeelectrode; contacting the tissue with the plasma (124) and therebyavoiding exposing the tissue to electric fields generated between theactive electrode and the return electrodes.

Now referring generally to the embodiments shown in FIGS. 13-16, anelectrosurgical system (150) for insertion into a body structure (138)is provided. Electrosurgical system (150) generally includes shaft (152)having a distal end (156) and a proximal end (not expressly shown) wheredistal end (156) is adapted for treating a target tissue within bodystructure (138). In a preferred embodiment, body structure (138) may bean intervertebral disc and the target tissue comprises tissue withineither or both the nucleus pulposus or the annulus fibrosus thereof. Inthe present embodiment distal end (156) includes an active electrode(158) disposed on the exterior surface of shaft (152). Also disposedwithin distal end (156) but within shaft (152) is a return electrode(160) that is insulated from the active electrode by an insulatingmember or spacer (162). In this position, insulating member (162)prevents direct electrical contact between active electrode (158) andreturn electrode (160) but also allows conductive fluid (172) to flowtherebetween. Also included in shaft (152) are suitable electricalconductors (not expressly shown) adapted for connection with aradio-frequency voltage source and applying a radio-frequency voltagedifference across active electrode (158) and return electrode (160) anda conductive cap (177), as described below.

In the present embodiment apparatus (150) comprises a fluid deliverylumen (170) and an aspiration lumen (171). Fluid delivery lumen (170) ispreferably adapted to supply an electrically conductive fluid (172) suchas saline, Ringer's solution or another suitable biocompatible ionicsolutions to the distal end (156) of shaft (152) in the vicinity of theelectrodes (158) and (160) and the target tissue. As is illustrated inFIGS. 1 and 11, electrically conductive fluid (172) may be supplied froma reservoir (26A) in communication with the apparatus (150) at theproximal end or from another suitable source of electrically conductivefluid. In the present embodiment the distal terminus of delivery lumen(170) comprises return electrode (160).

In the present embodiment fluid delivery lumen (170) is connected withand terminates within an interconnecting passage or chamber (168) formedwithin the distal end (156) of the shaft (152) between the activeelectrode (158) and return electrode (160). In other words, fluiddelivery lumen (170) supplies fluid (172) to chamber (168) which maythen preferably flow through apertures (178) of active electrode (158).Within chamber (168), when a suitable high frequency voltage is appliedacross the electrodes (158) and (160) in the presence of electricallyconductive fluid (172) a plasma may preferably be formed for thetreatment of tissue proximate active electrode (158).

Shaft (152) also includes aspiration lumen (171). In the presentembodiment aspiration lumen (171) includes a distal opening (186)proximate active electrode (158), return electrode (160) and chamber(168) as well as a plurality of apertures (188) formed along a selectedlength (182) of shaft (152). In the present embodiment, apertures (188),which may also be referred to as “inlet apertures”, are substantiallyuniformly spaced along selected length 182, including being uniformlyspaced along the circumference of shaft (152), and have a uniform size.In alternate embodiments the size and disposition of apertures (188) mayvary along the selected length. In the present embodiment, selectedlength (182) comprises approximately 2.5 centimeters, however inalternate embodiments selected length may be in the range of betweenabout one centimeter and about five centimeters or between about twocentimeters and about three centimeters.

As shown in the embodiment of FIG. 14, conductive fluid (172) isdelivered through fluid delivery lumen (170) and fluids are vented fromthe treatment site via aspiration lumen (180). Fluids may enteraspiration lumen (180) through opening (186) or apertures (188) andsubsequently travel away from the body structure (138) in the directionof arrows (181).

Referring now to FIG. 13, the selected length (182) comprises a firstportion (183) and a second portion (184) where the first portion (183)is designed to be inserted within body structure (138) during a medicalprocedure while the second portion (184) is designed to remain outsideof the body structure during use. For example, first portion (183) maybe about one (1) centimeter and second portion (184) may be about oneand one-half (1.5) centimeters. In this manner, first portion (183)allows fluids (including gases) produced during treatment of the targettissue to evacuate through aspiration lumen (180) via apertures (188)and opening (186) along first portion (183). In an alternate embodiment(not expressly shown) the cumulative or collective area of apertures(188) with second portion (184) is at least equal to the cross sectionalarea of aspiration lumen (180). In another alternate embodiment, thesize and/or distribution of apertures (188) in the first portion (183)may be greater than the size and/or distribution of apertures (188) inthe second portion (184). In an alternate embodiment, distal opening 186may be filled with an epoxy or other suitable material such that flowinto aspiration lumen 180 is provided only through apertures (188).

By providing second portion (184) outside of body structure (138)pressure P₁ within body structure may be preferably kept at orsubstantially near atmospheric pressure. Aspiration lumen (180) maypreferably be in communication with a suction source, however, thedisposition of apertures (188) along selected length (182) allows fluidto flow away from the treatment site without requiring a separatesuction source. In situations in which a separate suction source is notprovide or not used, the evacuated material may exit aspiration lumen(180) via apertures along the second portion (184) of selected length(182).

As noted above, when the power is applied to electrodes (158) and (160),an electric field (not expressly shown) may be is generatedtherebetween. However, since this electric field is directed inwards andis maintained primarily within the distal end (156) the effect of theelectric field on neighboring tissue is substantially minimized, if noteliminated.

In the embodiments of the apparatus illustrated in FIGS. 13-16, returnelectrode (160) is in electrical communication with a conductive cap ortip (177) having an exposed surface on the outer surface of the shaft(152), such that the cap is sufficiently spaced with respect to activeelectrode (158) to minimize generation of an electric field between theactive electrode and the cap. As discussed above, an advantage ofproviding conductive cap (177) is to ensure that the charge density onthe surface of return electrode (160) is lower than the charge densityon the surface of active electrode (158).

As shown in FIG. 16, active electrode (158) includes a screen or meshportion (196) comprising a plurality of apertures (178). Activeelectrode (158) also includes a distal loop assembly (196). As shown inFIG. 15, loop assembly (196) is adapted to interface with distal end(156) of shaft (152). As shown, bushing (190) is disposedcircumferentially around the exterior surface of return electrode (160).Note that in FIG. 15 a proximal portion of bushing 190 has been cut awayto allow return electrode (160) and chamber (168) to be in view. In thepresent embodiment bushing (190) preferably extends slightly in aproximal direction such that loop section (196) may then be disposedaround bushing (190) and such that bushing (190) insulates loop (196)from return electrode (160). A distal spacer (192), also shown in FIG.15 with a portion removed, may be further provided circumferentiallyaround bushing (190) to insulate cap (177) from active electrode (158).Distal spacer (192) and cap (177) may aid in blunt dissection andprotect active electrode (158) during insertion into body structure 138.In an alternate embodiment active electrode (158) may be brazed ontodistal end (156) of shaft (152). In an alternate embodiment electrode(158) may include a second loop located, for example, at the oppositeend of screen (194) for interfacing with distal end (156).

As shown in FIGS. 13-15 an electric insulator or spacer element (162) isprovided between active electrode (158) and return electrode (160).Insulator (162) includes an opening for allowing conductive fluid toflow between active electrode (158) and return electrode (160).Additionally, insulator (162) may include apertures (163) formedtherein. Apertures (163) may be formed uniformly on the body of theinsulator (162) or may be provided along only a portion of insulator(162). Apertures (163) may be elliptical (as shown), circular or haveany other suitable shape. Apertures (162) may open into chamber (168)and/or onto a surface of return electrode (160). In this mannerapertures (163) may contribute to ensuring that the charge density onthe surface of return electrode (160) is lower than the charge densityon the surface of active electrode (158). Apertures (163) preferablyprovide an exit path for conductive fluid (172) in chamber (168) in theevent that screen portion (194) of active electrode (158) becomesclogged.

By the present description and Figures it is to be understood that theterms used herein are descriptive rather than limiting, and thatchanges, modifications, and substitutions may be made without departingfrom the scope of the invention. Also it will be appreciated thatalthough the present apparatus, system is described in the contextelectrosurgery on an intervertebral disc, the apparatus and its use isnot restricted to treating discs but is applicable in general forelectrosurgical procedures wherein is desired to minimize exposure ofthe tissue to electrical stimulation, and where access to the tissue islimited. Therefore the invention is not limited to the embodimentsdescribed herein, but is defined by the scope of the appended claims.

1. An electrosurgical apparatus comprising: a shaft having a proximalend portion and a distal end portion; an active electrode disposed onthe surface of the distal end portion of the shaft; a return electrodedisposed within the distal end portion of the shaft; an insulatingmember positioned on the distal end portion of the shaft and preventingdirect electrical contact between the active and return electrodes;electrical conductors adapted for applying a radio-frequency voltagedifference across the active and return electrodes, wherein the activeelectrode and return electrode define an interconnecting passagewaywithin the distal end portion of the shaft; and wherein the shaftcomprises an aspiration lumen having a plurality of inlet aperturesformed along a selected length of the shaft.
 2. The electrosurgicalapparatus of claim 1 wherein the selected length is between about onecentimeter and about five centimeters.
 3. The electrosurgical apparatusof claim 1 wherein the selected length is between about two centimetersand about three centimeters.
 4. The electrosurgical apparatus of claim 1wherein the selected length of the shaft comprises a first portion forinsertion within a target tissue structure and a second portion forventing outside of the target tissue structure.
 5. The electrosurgicalapparatus of claim 4 wherein the target tissue structure comprises anintervertebral disc.
 6. The electrosurgical apparatus of claim 4 whereinthe collective area of the apertures in the second portion of theselected length is at least equal to a cross sectional area of theaspiration lumen.
 7. The electrosurgical apparatus of claim 1 whereinthe aspiration lumen is in communication with a suction source.
 8. Theelectrosurgical apparatus of claim 1 wherein the aspiration lumen andthe plurality of apertures are adapted to allow fluid to flow away fromthe target tissue through one or more of the apertures without requiringa suction source.
 9. The electrosurgical apparatus of claim 1 whereinthe inlet apertures are substantially evenly spaced along the selectedlength of the shaft.
 10. The electrosurgical apparatus of claim 1wherein the inlet apertures are spaced along the circumference of theshaft.
 11. The electrosurgical apparatus of claim 1 wherein the activeelectrode comprises a screen section having a plurality of aperturesformed therein.
 12. The electrosurgical apparatus of claim 11 whereinthe active electrode comprises a distal assembly loop for interfacingwith the distal end portion of the shaft.
 13. The electrosurgicalapparatus of claim 11 wherein the active electrode is brazed onto thedistal end portion of the shaft.
 14. The electrosurgical apparatus ofclaim 1 further comprising an insulator separating the active electrodeand the return electrode.
 15. The electrosurgical apparatus of claim 14wherein the insulator comprises a plurality of apertures formed therein.16. An electrosurgical instrument for treating tissue within a body,comprising: a shaft having a proximal end portion and a distal endportion; an active electrode comprising a tissue-contacting surface onthe distal end portion of the shaft; a return electrode recessed withinshaft; and an insulator separating the active electrode and the returnelectrode, wherein the tissue-contacting surface is adapted forgenerating plasma upon application of a radio frequency voltage acrossthe active and return electrode in the presence of an electricallyconducting fluid; and wherein the shaft comprises an aspiration lumenhaving a plurality of inlet apertures formed along a selected length ofthe shaft, wherein the selected length of the shaft comprises a firstportion for insertion within a target tissue structure and a secondportion for venting outside of the target tissue structure.
 17. Theelectrosurgical instrument of claim 16 wherein the selected length isbetween about one centimeter and about five centimeters.
 18. A systemfor performing an electrosurgical procedure on a target tissue within abody structure using plasma, the system comprising: an electrosurgicalinstrument comprising a shaft; an electrically conductive fluid supplyhaving a discharge port on a distal end of the shaft; and aradio-frequency voltage supply connected to the electrosurgicalinstrument, wherein the shaft comprises: an active electrode on thedistal end; a return electrode recessed within the shaft; an electricalinsulator separating the active and return electrode; and wherein theshaft comprises an aspiration lumen having a plurality of inletapertures formed along a selected length of the shaft, wherein theselected length of the shaft comprises a first portion for insertionwithin a target tissue structure and a second portion for ventingoutside of the target tissue structure.
 19. The electrosurgicalapparatus of claim 18 wherein the active electrode comprises a screensection having a plurality of apertures formed therein.
 20. Theelectrosurgical apparatus of claim 18 wherein the active electrodecomprises a distal assembly loop for interfacing with the distal endportion of the shaft.